Milliohm resistors for car dome light?

I'm trying to create this circuit for a dome light. I need resistors smaller than 1 ohm to draw 1500 ma out of it. I'm planning on running to Lux III's. Do I hook them up in series?

Close - paralleling resistors lowers the total resistance.
Rnew= 1/(R1 + R2 + R3...)

However, the circuit you're looking at would require .8333 ohms; .82 ought to be a common value, so a single resistor would suffice.
Thing is, you're looking at 1.875 watts through the resistor, so a big power resistor will be required, and you'll definitely want to heatsink the regulator, and probably the resistor.

The Luxeons (in series, BTW), will also be pushing a lot of heat at that level, which seems like a lot for a dome light for practical use. The overall efficiency will be pretty low, too, not that it matters so much in a vehicle.

Best,
Jon

hyperslug said:

I'm trying to create this circuit for a dome light. I need resistors smaller than 1 ohm to draw 1500 ma out of it. I'm planning on running to Lux III's. Do I hook them up in series?

Click to expand...

I agree that 3 luxes would be overkill for a dome light. I use 8 20mA (40cd)LEDs in 2 chains of 4 and they are perfectly fine for reading by.

With 14v available while the car is in motion, it is MUCH more advisable to hook 3 Lux's in series and keep the original circuitry. Then all the Lux's will have the same current through them regardless of binning. Besides, if you tried to drop 8 volts while pushing 1.5A through the 317; you're asking it to dissipate 12 watts, which would cook the device unless you attach it to a hunk of heat-sinking the size of the dome light itself!

dont know about resistors but here is a place that has pre made dome lights. unless you want to do it yourself.

http://www.superbrightleds.com/cgi-bin/store/commerce.cgi?product=CAR&keywords=&cart_id=5570945.17784&next=50